Ignition system for internal combustion engine

Abstract

An ignition system for an internal combustion engine is widely known which includes a primary current control switch circuit adapted to be turned off at an ignition position to interrupt flowing of a primary current through an ignition coil, to thereby induce a high voltage for ignition across the ignition coil. Continuation of the flow of the primary current causes an increase in power consumption and generation of heat from the ignition coil. An ignition system of the present invention utilizes charging and discharging of a control capacitor to permit control over the time for which the primary current is flowing to be accomplished with a simple structure. A discharge resistor which is arranged in parallel with the control capacitor carries out discharge of the control capacitor to interrupt the flow of the primary current when the internal combustion engine is stopped.

What is claimed is: 
     
       1. An ignition system for an internal combustion engine comprising: at least one ignition coil;   a signal coil for generating a first signal at a position of which a phase is advanced relative to an ignition position of the internal combustion engine and a second signal at said ignition position;   a control capacitor;   a charging circuit for charging said control capacitor when said first signal is generated;   a discharge circuit for causing discharge of said control capacitor when said second signal is generated;   a discharge resistor connected in parallel with said control capacitor;   a switch circuit for controlling a primary current which is turned on to cause a primary current to flow from a power supply to said ignition coil when a voltage across said control capacitor rises and turned off to interrupt said primary current when said voltage falls.   
     
     
       2. An ignition system for an internal combustion as defined in claim 1, wherein said charging circuit comprises a waveform shaping circuit for generating a first pulse signal for a period of time during which said first signal exceeds a predetermined threshold level; and a charging switch circuit kept turned on to charge said control capacitor by means of a voltage from said power supply while said first pulse is being generated.   
     
     
       3. An ignition system for an internal combustion engine as defined in claim 1, wherein said discharge circuit comprises a waveform shaping circuit for generating a first pulse signal for a period of time during which said first signal exceeds a predetermined threshold level; and a discharge switch circuit driven by said second pulse signal to be turned on, to thereby instantaneously carry out discharge of said control capacitor.   
     
     
       4. An ignition system for an internal combustion engine as defined in claim 1, wherein said discharge resistor has a resistance value sufficient to effectively prevent discharge of said control capacitor until said second signal is generated while the internal combustion engine is being properly actuated. 
     
     
       5. An ignition system for an internal combustion engine as defined in claim 1, wherein said primary current control switch circuit comprises a reference voltage generating circuit;   a comparison circuit for carrying out comparison between a reference voltage from said reference voltage generating circuit and a voltage of said control capacitor; and   a primary current control semiconductor switch element connected in series to a primary winding of said ignition coil and driven by a signal supplied from said comparison circuit.   
     
     
       6. An ignition system for an internal combustion engine as defined in claim 1, wherein said primary current control switch circuit comprises a semiconductor switch element of a large input impedance. 
     
     
       7. An ignition system for an internal combustion engine as defined in claim 5, wherein said semiconductor switch element is a field effect transistor. 
     
     
       8. An ignition system for an internal combustion engine comprising: an ignition coil;   a pulser coil for generating a first signal at a position of which a phase is advanced relative to an ignition position of the internal combustion engine in synchronism with rotation of the internal combustion engine;   a control capacitor;   a charging circuit for charging said control capacitor when said first signal is generated;   a discharge circuit for causing discharge of said control capacitor when a second signal is generated;   a discharge resistor connected in parallel with said control capacitor;   a primary current control transistor switch circuit in which a voltage across said control capacitor is used as a control voltage and which is turned on to cause a primary current to flow from a power supply to said ignition coil when said control voltage rises and turned off to interrupt said primary current when said control voltage falls.